The present invention has to do with cold working metal and relates in particular to a method and an apparatus for reforming burred, crossed or mutilated threads on cylindrical workpieces.
The invention also relates to a method and apparatus for cold working the exterior surface of a machined workpiece to increase the effective diameter of the workpiece or to reduce the diameter of a flared end of a tubular workpiece.
Prior art methods and devices which are related to the present invention are disclosed and described in U.S. Pat. No. 981,642, issued Jan. 17, 1911 to Dreier, U.S. Pat. No. 1,017,403, issued Feb. 13, 1912 to Garbarino et al., U.S. Pat. No. 1,085,643, issued Feb. 3, 1914 to Tewksbury and U.S. Pat. No. 1,506,027, issued Aug. 26, 1924 to O'Brien.
The '642 patent shows a set of pipe thread cutting rollers 6. The '403 reference shows a rethreading to tool comprising a number of single land, disc-shaped members 17. The '643 patent shows rollers E for cutting pipe threads and the '027 reference shows a series of discs 16 mounted on inclined spindles 15 to accommodate the lead of threads being restored.